US 3252812 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
United States Patent 3,252,812 GLASS COMPOSITIONS Stphane Dufaure dc Lajarte, Paris, France, assignor to Compagnie do Saint-Gobain, Paris, France No Drawing. Filed Italy 5, 1957, Ser. No. 669,956 Claims priority, application France, July 10, 1956,
3 Claims. (er. 106-52 the slightest devitrification is produced, the presence of devitrified particles being entirely excluded, particularly in the manufacture of tempered objects.
The viscosity of the novel glasses at fusion temperature is low enough to permit easy preparation under conditions that assure excellent homogenity. Furthermore, their resistance to attack by water is so high that it prevents any substantial reduction, by weathering, of the surface resistance of insulators made from the glass.
The examples which follow compare a prior art glass of a standard composition :for electrical insulators, denominated A, with glasses B, C, D which conform to this invention, as to their devitrification and resistance to perforation by voltage at high temperature. The latter quality was measured on plates A, B, C, D of 500 X 500 x 7 mm, which had been polished and tempered and kept at 'uniform temperature of 200 C. in an electric furnace. The voltagewas applied to the center of these plates by two circular metal electrodes of mm. diameter soldered to the glass by metal solder to prevent the intrusion of air, one of the electrodes too high an upper limit of devitrification; or it may have a temperature and speed of crystallization such as to permit the formation of devitrified particles during its transformation into useful articles by normal processes, and such devitrified particles must be entirely avoided, in particular for the manufacture of tempered articles; or its resistance to weather and water may be so low that its surlicial resistance becomes lower after use out-- doors, for instance as an insulator.
An object of this invention is to make glass which has high resistance to perforation by high-voltage electric current, particularly when the glass is hot.
Another object is to provide such glass with an upper limit of devitrification, a temperature and speed of crystallization, sufficiently low so that, glass objects free of devitrified particles can be produced therefrom by working under customary conditions.
Another object is to provide such glasses having good workable viscosity in the temperature ranges customarily used in the industry for fabricating objects of electrical utility.
Another object is to provide such glasses with good resistance to attack by water, weather, and current, so that parts exposed outdoors, such as insulators, may retain their high resistance at all times and over long periods.
These objects are accomplished, generally speaking, by a glass having the composition by weight Percent SiO +Al O (A1 0 not being over 8%) 68-75 Na O+K O (Na O not being over 13% when A1 0 is over 4% and not over 11% when A1 0 is less than 4%) 12-15 CaO+BaO+MgO (CaO being between 7 and 12% and BaO absent if desired) 12-16 Other metal oxides of glass-making grade, of which B203, F6203, ZIOz, T102, M110 and are examples, and fluorine compounds 0-5 These glasses are made in standard furnaces by standand melting, .finin-g, conditioning and working techniques, the particular degrees of which are not part of this invention. When glass objects of the new compositions are made by hand or by automatic techniques, they have better resistance to perforation by electric current when hot than do the glass compositions of the prior art when made by like techniques.
The novel glasses have an upper limit of devitrification, a temperature and a speed of crystallization low enough so that, under the usual working conditions not being encircled by a ring for distributing the potential fixed to the glass in the same way. The current, perfectly sinusoidal, having a frequency of 50 periods per second, was increased every 10 seconds by increments of 5 kv., from 0 until perforation occurred.
A B O D Upper limit, C 1,070 1, 1, 146 1,120 Temperature of maximum rate of crystallization, C 976 1, 016 1, 047 1,000 Speed of, at maximum rate, in microns/minute 5.1 7.5 11.6 3 Resistance to Perforation at 200 C,
The foregoing glasses were made under the temperature conditions shown in the table, were poured on a table, cooled, ground, polished, and tempered, all by standard techniques.
The glasses of this invention have higher resistance to perforation by electric current, compared to standard insulators of the prior art, of which glass A is typical. No substantial changes in conditions of manufacture are required by the characteristics of devitrification of the new glasses, which is advantageous in itself.
As many apparently widely different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments.
What is claimed is:
1. Electrically insulating glass having a composition consisting essentially of the following constituents in percent by weight:
sio 66.8 B203 .rsoooarsw' SiO 68.1
Fe O 0.8
CaO 10 MgO 2 BaO 3 said glass having resistance to perforation equivalent to at least about 31 kv. in a plate 500 X 500 x 7 mm., at 200 C., under 50 cycle alternating current.
3. Electrically resistant glass, in particular for glass insulators, having a resistance to perforation equivalent to at least about 20 kv. in a plate 500 x 500 x 7 mm. at 200 C., under sine wave current of 50 periods, and having a composition consisting essentially of Members from the group consisting of CaO, MgO,
' Wt. percent SiO +Al O of which Al O is always present and is lower than 8% 6875 Na O+K O, both being present 12-15 and Na O is not over 1 11 Na O is not over 2 13 and E210, of which CaO and E210 are present 1216 and C210 is in the range 7-12 Metal oxides of the type of B 0 Fe O ZrO I TiO PbO, MnO, ZnO+fluorine compounds--- 0-5 When A1203 is less than 4%- When A1203 is greater than 4%.
References Cited by the Examiner UNITED STATES PATENTS 2,443,142 6/1948 Lyle 10652 2,508,070 5/1950 Lyle 10652 2,552,495 5/1951 Poole 106-52 OTHER REFERENCES Glastechnische Tabellen (1932), p. 635 (Etel-Pirani- Scheel) #209.
TOBIAS E. LEVOW, Primary Examiner.
JOHN R. SPECK, JOSEPH REBOLD, Examiners.